1. Field of Invention
The present invention pertains to products and processes useful in the fields of development, genetics, and transcription biochemistry. The invention is generally useful in the diagnosis and treatment of dermatologic conditions.
2. Description of the Related Art
Although hair loss is a problem of great interest to dermatologists and the lay public, basic knowledge of the biology of hair growth and maintenance has been limited.
In most mammals, hair does not grow continuously but undergoes cycles of activity involving periods of growth, rest, and shedding. On the human scalp, from 100,000 to 350,000 hair fibers or shafts undergo metamorphosis in three distinct stages:    (a) the growth phase (anagen) during which the hair root bulb or dermal papilla (also called the “follicular papilla”) penetrates deep into the dermis with the cells of the bulb dividing rapidly and differentiating in the process of synthesizing keratin, the substance of the hair shaft itself. In normal humans, this growth phase is thought to last from one to five years;    (b) the transitional phase (catagen) is marked by the cessation of mitosis and lasts from two to three weeks; and    (c) the resting phase (telogen) where the hair is retained within the scalp for up to 12 weeks before the emerging new hair developing below it dislodges the telogen-stage shaft from its follicle.
Experiments with mouse hair follicles showed that the anagen-stage stem cells, stored within the bulge area of the follicle, proliferate during early anagen and migrate to the root bulb region prior to differentiation. See U.S. Pat. No. 5,279,969. The bulge cells can be stimulated to proliferate in response to physical and chemical stimuli causing telogen follicles to commence anagen. In addition, the physical proximity of the follicular papilla to the stem cell-containing bulge area plays a role in the onset of the anagen stage. It has been speculated that damage to the bulge region results in permanent alopecia, whereas damage to the hair root bulb alone results in alopecia areata and is temporary.
It is generally accepted that genetic hair loss arises from activation of an inherited sensitivity to circulating androgenic hormones. Such androgenic alopecia is the single most common type of recognizable alopecia to affect both men (50%) and women (30%), primarily of Caucasian origin. Gradual changes in the width and length of the hair shaft are experienced over time and with increasing age, prematurely in some. Terminal hair is gradually converted to short, wispy, colorless vellus hair. As a consequence, men in their 20's and women in their 30's and 40's begin to notice their hair becoming finer and shorter. In addition, the ratio of growing hairs to hairs in the resting and shedding phases declines from as high as 9:1 to as low as 2:1.
Androgenic alopecia, or male pattern baldness, is largely the result of heredity, advancing age, and male hormone secretion, specifically the hormone dihydrotestosterone (DHT). At advanced stages, male pattern baldness is characterized by a bald scalp at the crown of the head and a horseshoe shaped fringe of hair remaining on the sides of the head. Male pattern baldness may be mediated by time-dependent, steroid hormone-regulated gene expression that results in a diminution in the growing phase of scalp hair.
Minoxidil, a potent anti-hypertensive medication, has been used with limited success to treat male pattern baldness by topical application to the scalp. See U.S. Pat. Nos. 4,139,619 and 4,596,812. A 2% or 5% solution containing alcohol and polyethylene glycol is used. One theory for its mode of action is that blood vessels are dilated and the increased blood supply stimulates nourishment of hair follicles. Many patients, however, do not achieve a satisfactory result (younger patients and patients with less hair loss have better results), the degree of new hair growth is usually minimal, and the area of the scalp that is affected is usually limited to the vertex cranii. Minoxidil's effectiveness for the treatment of androgenic alopecia may be limited because it does not reduce production of the hormones responsible for causing male pattern baldness.
Therefore, another approach for treating male pattern baldness has been the administration of agents which inhibit the conversion of testosterone to DHT. Testosterone binds specifically to the 5 alpha-reductase enzyme which converts testosterone to its active metabolite DHT. In turn, DHT binds to nuclear receptor proteins and may regulate the synthesis of specific proteins which lead to male pattern baldness.
An orally administered inhibitor of 5 alpha-reductase currently prescribed for the treatment of male pattern baldness is finasteride, a synthetic 4-azasteroid compound. See U.S. Pat. Nos. 4,377,584; 4,760,071; 5,547,957; and 5,571,817. Finasteride is more conveniently administered than minoxidil and is more effective than minoxidil in treating androgenic alopecia. However, finasteride also has undesirable effects which include reducing libido, erection, and semen volume in men; and causing fetal defects in pregnant women.
A genetic approach to developing pharmaceutical candidates is to screen small molecules for modulation of transcription factor activity which regulates hair growth and/or maintenance. For example, Tularik has described high-throughput assays for screening candidate chemical agents which modulate transcription mediated by sequence-specific transcription factors. But a human transcription factor essential to the growth and/or maintenance of hair was not available until the invention described in the present application.
For all of the above reasons, it was necessary to develop molecular probes and genetic models for hair loss. In hr/hr (hairless) mutant mice, initial hair growth is normal but, after the first wave of shedding, hair fails to grow back and complete loss of hair results. In this respect, the development of hair loss resembles alopecia universalis caused by a rare inherited mutation in humans (see Ahmad et al., Science, 279, 720-724, 1998; Cichon et al., Hum. Mol. Genet., 7, 1671-1679 and 1987-1988, 1998). In addition, mutant mice show increased sensitivity to ultraviolet (UV) radiation and chemical-induced skin carcinogenesis. The human Hairless gene is identified and characterized herein.